A pensioner suspected of being Russia's worst-ever serial rapist has been jailed for 18 years after he admitted he "treated himself to women on his birthday".

Perverted Valery Makarenkov, 69, was convicted of 31 violent sex attacks but police are investigating allegations of many dozens of further cases.

He has confessed to raping 90 women and underage girls but investigators believe his true tally is at least 108.

Wearing a black cap, he attacked his victims from behind after cycling up behind them and dragging them into bushes.

His first attack was 43 years ago and Moscow detectives and criminologists checked the details of 26,000 men before he was detained in May 2014 in the city's Kuzminki Park.

Makarenkov told police he liked to "treat" himself to sex attacks on his birthday (Image: CEN)

The evil attacker has been branded the "birthday sex maniac" and the "cycling rapist".

He admitted to police that he "treated himself to women on his birthday" and snared victims while riding his Soviet-era Salut bicycle.

"I gave myself these girls as a birthday gift", he was reported to have said.

He also stole items from his victims which he kept as souvenirs at his cramped flat - examples included a child's badge, toys, a doll and a tin of peas.

His youngest victim was believed to have been aged ten.

Now divorced, he told police his first rape was a teenage girl in 1973 after his wife refused to have sex following childbirth.

Working as a part-time taxi driver, he claimed he was twice "drugged" by women .

He attacked the women in Moscow (Image: Getty)

These incidents led to a "grudge against all women".

Makarenkov was sentenced to 18 years in prison in a maximum security penal colony but police continue to probe his alleged crimes, including fears that he murdered at least three times.

"The investigation of other crimes - attacks on woman, violent assaults and murders - is on-going and Makarenkov will be checked for involvement," said a statement from Russia's Investigative Committee, equivalent of the FBI.

"At night or in early morning he followed his victims on his bike in backyards and parks, attacked from behind, strangled them but not to death, then raped and stole valuable belongings.

"Usually his attacks took place from May to October when it was possible to go around on a bike.

"For a long time Makarenkov managed to hide well from police because he acted in different districts of Moscow. "

He "almost never committed two crimes in one area.

"About 20,000 Muscovites were checked in connection to Makarenkov's crimes before he was caught."

A source added: "In Makarenkov's case there were several factors: hyper-sexuality, along with love of risk and danger.

"He was often stopped for dangerous and drunk driving. He enjoyed being a hunter.